A perpendicular magnetic recording system using a magnetic recording medium having an axis of easy magnetization perpendicular to the surface of the magnetic layer thereof has recently been proposed. This perpendicular magnetic recording system is said to be substantially very suitable for high density recording, since in this system, the higher the recording density becomes, the greater the reduction in the demagnetization field of a magnetic recording medium, resulting in excellent reproduced output.
A magnetic recording medium having an axis of easy magnetization perpendicular to the surface of a magnetic layer thereof is needed to perform perpendicular magnetic recording. In this connection, the perpendicular magnetic recording medium comprises a base or a support composed of non-magnetic materials such as high molecular weight materials or non-magnetic metals having coated thereon Co-Cr alloy and the like by a sputtering method or the like.
Also the perpendicular magnetic recording medium of so called two layered type is known, wherein a layer with high magnetic permeability composed of soft magnetic materials such as, for example, a permalloy layer (Ni-Fe type alloy) is provided under the perpendicular magnetic layer composed of Co-Cr alloy as described above to improve the recording and reproducing efficiency during perpendicular magnetic recording and reproducing.
Flexible disks and the like using the above described perpendicular magnetic recording system, employ a dual perpendicular magnetic recording medium of the two layered type wherein the above described under layer is provided on both surfaces of the support and is excellent since such perpendicular magnetic recording medium can contain voluminous recorded information and curling can easily be improved for the floppy disk.
Both the perpendicular magnetic recording medium and the dual perpendicular magnetic recording medium can be prepared by coating the above described materials continuously or discontinuously on a support using a sputtering apparatus.
The above described perpendicular magnetic recording medium can largely be expected to be used as a magnetic tape and as a magnetic disk, because it is suitable for high density recording. However, such medium generally has a serious problem of poor running durability. For example, in case of a perpendicular magnetic recording disk provided with Co-Cr alloy layer, running can not often be continued beyond about 10,000 passes because of coagulation occurring on the surface of the alloy layer.
To solve the above problem, it has been proposed to provide a protective layer made of carbon, SiO.sub.2 and BN, as disclosed in Japanese Patent Application (OPI) No. 133627/1983. The term "OPI" as used herein means an "unexamined published application". Alternatively, SiC, as disclosed in Japanese Patent Application (OPI) No. 130437/83 may be applied on the surface of a magnetic layer by a sputtering method.
However the above proposal to improve the running durability is not satisfactory and there is still the problem that the reproducing property of products manufactured using the same manufacturing steps is poor, that is, excellent durability can not always be obtained.
Accordingly, an object of the present invention is to provide a perpendicular magnetic recording medium having a good reproducing property and largely improved running durability.